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Tryptic Digestion of Muscle Components Simulates Many of the Changes Caused by Postmortem Storage¹

Iowa State University,^,4 Ames 50010

Abstract

The effects of trypsin on subcellular components purified from muscle cells were compared with the effects of postmortem storage on these same components. The results show that: 1) limited trypsin digestion and postmortem storage both cause a small increase in the Ca²⁺-stimulated, Mg²⁺-dependent ATPase activity of fragmented sarcoplasmic reticulum; 2) both limited trypsin treatment and postmortem storage cause almost complete loss of the Ca²⁺-sequestering abilities of fragmented sarcoplasmic reticulum; 3) trypsin treatment and postmortem storage both cause an increase followed by a decrease in the Mg²⁺-modified ATPase activity of myofibrils; the Ca²⁺-modified ATPase activity increases and then remains constant during either trypsin treatment or postmortem storage; 4) very brief trypsin digestion and postmortem storage both increase the rate of turbidity development in actomyosin preparations following the addition of ATP; 5) both limited trypsin treatment and postmortem storage cause shortened sarcomeres to lengthen in the absence of ATP; and 6) brief trypsin digestion and postmortem storage both produce degradation of the Z-disk. These striking similarities between the effects of trypsin and the effects of postmortem storage show how proteolysis may be an important factor in postmortem alterations in muscle cells, but they do not prove that proteolysis is actually involved in postmortem muscle alterations.

¹ Journal Paper No. J-6893 of the Iowa Agriculture and Home Economics Experiment Station, Projects 1549, 1795 and 1796. This research was supported in part by Public Health Service Research Grants No. GM-12,488 and AM-12,654. R. M. Robson was a predoctoral fellow of the Public Health Service, Division of General Medical Sciences. We express our sincere appreciation to Dr. F. C. Parrish for helpful discussions, to Dr. D. W. Henderson for some electron microscopy of postmortem muscle, to Marilee Webb and Barbara Wallner for darkroom assistance, and to Karen Schwarz for assistance with the manuscript.

² Present address: Muscle Biology Section, 124 Animal Science Laboratory, University of Illinois, Urbana 61801.

³ Present address: Swift and Co., 1919 Swift Drive, Oak Brook, Illinois 60521.

⁴ Muscle Biology Group, Departments of Animal Science, Biochemistry and Biophysics, and Food Technology, Cooperating.